DataSheet_1_Exposing Atlantic Salmon Post-Smolts to Fluctuating Sublethal Nitrite Concentrations in a Commercial Recirculating Aquaculture System (RAS) May Have Negative Consequences.docx

Salmon farmers are interested in extending the time post-smolts are reared in recirculating aquaculture systems (RAS). However, there is a lack of knowledge regarding optimal water quality for post-smolts in RAS, and regarding potential consequences of long term exposure to different toxic compounds, such as nitrite, in the RAS water. To address this issue, we conducted a case study at a Faroese Atlantic salmon farm, that rears large post-smolts in fresh water RAS for 22 months before sea transfer, with no additional chloride salt, a known treatment for nitrite toxicity. The aim was to document the potential effects of long-term exposure of fluctuating sub-lethal nitrite concentrations in fresh water RAS on blood physiology of large post-smolts. The study was conducted over six weeks, at the end of the RAS production cycle. Our case study shows that after ~22 months in RAS with no additional chloride, the fish had accumulated a plasma nitrite concentration 8 to 16 times higher than the ambient water. Our results indicate that the accumulation may have resulted in extracellular hyperkaliemia, since there was a positive correlation between plasma nitrite and potassium levels (p=0.00095), with potassium levels almost twice as high than previously reported for Atlantic salmon. This could indicate that Atlantic salmon health is challenged due to prolonged sub-lethal nitrite exposure in fresh water RAS. Further research related to long-term nitrite exposure in RAS is needed to asses the potential negative impact, in order to optimize welfare and growth performance during production of Atlantic salmon post-smolts.

大西洋鲑养殖从业者希望延长幼鲑（post-smolts）在循环水产养殖系统（Recirculating Aquaculture Systems, RAS）中的培育时长。然而目前针对RAS内幼鲑的最优水质标准，以及该系统水环境中长期暴露于亚硝酸盐等各类有毒化合物的潜在影响，仍缺乏足够的科学认知。为解决这一问题，我们在一家法罗群岛大西洋鲑养殖场开展了案例研究：该场采用淡水RAS养殖大型幼鲑，在移养至海水前的培育周期长达22个月，且养殖过程中未添加用于缓解亚硝酸盐毒性的常规药剂氯化物。本研究旨在明确淡水RAS中波动的亚致死浓度亚硝酸盐长期暴露对大型幼鲑血液生理指标的潜在影响。研究于RAS生产周期末期开展，时长共计六周。本次案例研究显示，在未添加氯化物的RAS环境中养殖约22个月后，试验鱼的血浆亚硝酸盐浓度为环境水体的8至16倍。结果表明，该亚硝酸盐累积可能引发细胞外高钾血症：血浆亚硝酸盐浓度与钾离子水平呈显著正相关（p=0.00095），且钾离子浓度较既往大西洋鲑的报道值高出近一倍。这提示，淡水RAS中长期暴露于亚致死浓度亚硝酸盐，可能对大西洋鲑的健康状态造成负面影响。未来需开展更多针对RAS中长期亚硝酸盐暴露的相关研究，以评估其潜在负面影响，进而优化大西洋鲑幼鲑养殖阶段的福利水平与生长性能。